Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$167.64	6.168%	$177.98	$177.98	$178.00	$178.00
Purchase #2	$116.73	12.132%	$130.8917	$130.89	$130.90	$130.90
Purchase #3	$65.85	10.403%	$72.7004	$72.70	$72.70	$72.70
Purchase #4	$72.46	5.697%	$76.588	$76.59	$76.60	$76.60
Purchase #5	$67.42	3.475%	$69.7628	$69.76	$69.75	$69.80
Purchase #6	$91.76	9.120%	$100.1285	$100.13	$100.15	$100.10
Purchase #7	$92.87	8.301%	$100.5791	$100.58	$100.60	$100.60
7 purchase totals =	$674.73		$728.6305	$728.63	$728.70	$728.70